1. Field of the Invention
The present invention relates to a liquid crystal display including circular or polygonal polarizing plates each whose absorption and transmission axes have an improved precision in direction.
2. Description of the Related Art
Conventional laptop personal computers, mobile television receivers, cellular phones and the like include a rectangular display screen configured of a liquid crystal display.
As shown in FIG. 1, the liquid crystal display is provided with a rectangular polarizing plate 2 on the front surface of a substrate 1A, and similarly provided with the other rectangular polarizing plate (not illustrated; hereinafter referred to as a “rear polarizing plate”) on the unillustrated rear surface of the substrate 1B.
An absorption axis 2FK of the polarizing plate 2 is arranged vertical to an absorption axis 2RK of the rear polarizing plate. FIG. 1 illustrates the longest ones, arranged diagonally to each other, of the absorption axes 2FK and 2RK. The lengths of such absorption axes as well as the transmission axes vertical to the respective absorption axes are relatively long.
In general, under a high-temperature or high-temperature/high-humidity condition, PVA (polyvinyl alcohol) layers respectively of the polarizing plate 2 and the rear polarizing plate contracts in a direction of the absorption axes of the polarizing plate.
When phase difference plates are respectively attached to the polarizing plate 2 and the rear polarizing plate, the axial directions of each phase difference plate and the axial directions of the corresponding polarizing plate are misaligned from each other to a large extent, especially in a periphery of the display screen due to contraction of the PVA layer of the polarizing plate. As a result, display becomes uneven in the periphery (what is termed as a “picture frame”) of the display screen.
FIG. 2 shows the absorption axes 2FK and 2RK each arranged to stretch along either side of the display. The absorption axes 2FK and 2RK as well as their corresponding transmission axes are equal to each other in length, and are shorter than those shown in FIG. 1, and therefore the PVA layers contract to a smaller extent.
When a phase difference plate is attached to the polarizing plate 2 and the rear polarizing plate, a misalignment between the axial directions of each phase difference plate and the axial directions of the corresponding polarizing plate becomes small, the misalignment being caused by contraction of the PVA layer of the polarizing plate. As a result, it is possible to reduce display unevenness in the periphery (picture frame) of the display screen.
Recently, on the other hand, for the purpose of achieving higher contrast and resolution, there has been an increasing demand for improving the precision in the directions of transmission and absorption axes in polarizing plate relative to a liquid crystal layer.
When a rectangular polarizing plate is used, an inspection is performed to check whether a desired angle is formed between one side of the rectangle as a reference (hereinafter referred to as a “reference side”) and each of the absorption and transmission axes of the polarizing plate. After a polarizing plate which has passed this inspection is attached to the substrate, a similar inspection is performed to check whether a desired angle is formed between a reference direction of the substrate and the reference side of the polarizing plate.
Through these inspections, the precision in the directions of the respective absorption and transmission axes can be ensured.
Recent models of cellular phone often include a display screen in the shape of a circle or a polygon with five or more angles. Such a display screen is provided, for example, in the rear of the rectangular display screen.
In addition, there is a tendency in automobiles that display screens configured of a liquid crystal display are provided for indicators and front panel. For this reason, it is expected that display screens with various shapes will be demanded soon.
However, when a circular polarizing plate is used, the above-described inspections can not be performed because the circular polarizing plate has no reference side. As a result, it is likely that the direction of the absorption axis of the polarizing plate or the direction of transmission axis thereof may not be ensured with high precision.
Likewise, when a polygonal polarizing plate is used, the inspections can not be performed unless a reference side is defined. As a result, it is likely that the direction of the absorption axis of the polarizing plate or the direction of transmission axis thereof may not be ensured with high precision.
The present invention has been made with the foregoing points being taken into consideration. An object of the present invention is to provide a liquid crystal display including circular or polygonal polarizing plates each whose absorption and transmission axes have an improved precision in direction.